Wound Dressing Inhibiting Lateral Diffusion of Absorbed Exudate

ABSTRACT

A wound dressing including a hydrophilic layer and a hydrophobic layer is described. The hydrophilic layer absorbs exudate from a wound and the hydrophobic layer absorbs the exudate from the hydrophilic layer and traps the exudate. Because the hydrophilic layer is used adjacent to the wound, the exudate is readily absorbed thereby reducing the risk of maceration and infection of the wound tissue by the exudate. The hydrophobic layer receives the absorbed exudate from the hydrophilic layer and traps the exudate through an interaction that in turn prevents lateral diffusion of the exudate through the bandage to healthy portions of the skin. The hydrophilic and hydrophobic layers are fabricated from polymer fibers that can be spun to include components that facilitate wound healing, such as poly(hexamethylene biguanide) and/or hyaluronic acid.

BACKGROUND

The disclosure relates to a wound dressing having a structure thatabsorbs exudate from a wound and inhibits lateral diffusion of theexudate within the wound dressing, thereby reducing the exposure ofunwounded skin to exudate.

When skin is inflamed or wounded, areas of skin that are normallyrelatively dry may become unduly wet from the flow of liquid (exudate)discharged from the wound. The exudate from the wound can move overdrier and/or healthier skin areas. Also, deeper parts of the skinstructure that are normally wet and free of harmful microorganisms maybecome dry thereby risking infection from colonized bacteria due toexposure to open air and contaminants.

Conventional wound treatments apply a homogenous wound dressing (e.g.,one made of woven cotton threads) over the entire wound area primarilyfor the purpose of keeping the wound clean, absorbing some initialbleeding, protecting it from external contaminants, and/or protecting itfrom direct physical trauma.

FIG. 1 is a sectional diagram of a conventional wound dressing 10. Theconventional wound dressing 10 may be a gauze bandage or a multi-layerwicking bandage that wicks exudate from a wound approximately uniformlyin all directions. As the conventional wound dressing 10 becomessaturated by exudate at some locations, the exudate diffuse laterallythroughout the wound dressing. This lateral diffusion of exudate (asillustrated by arrows 14) to other regions of the wound dressing 10 canthen cause contact between healthy portions 18 of the skin and theexudate. This is problematic because the exudate may be contaminatedwith bacteria or other harmful substances, thereby infecting or injuringotherwise healthy portions 18 of the skin.

Furthermore, the conventional wound dressing 10 can become an antagonistto the wound 16 by not only maintaining contact between the wound and aportion of the conventional dressing that is saturated with exudate, butalso by adhering to healing portions of the wound. Upon removal of theconventional wound dressing 10, the healing portions of the wound 16 aredisturbed, delaying healing and increasing the risk of scarring.

SUMMARY

Embodiments relate to a wound dressing including a hydrophilic layerthat absorbs exudate from a wound and a hydrophobic layer that absorbsthe exudate from the hydrophilic layer and traps the exudate. Becausethe hydrophilic layer is used adjacent to the wound, the exudate isabsorbed thereby reducing the risk of maceration and infection of thewound tissue by the exudate. The hydrophobic layer receives the absorbedexudate from the hydrophilic layer and traps the exudate, which in turnprevents lateral diffusion of the exudate through the bandage to healthyportions of the skin. The hydrophilic and hydrophobic layers arefabricated from polymer fibers that can be spun to include componentsthat facilitate wound healing.

In one embodiment, the second fibrous polymer of the hydrophobic layerundergoes a volume reduction upon storing the exudate at inter-fibergaps.

In one embodiment, the first fibrous polymer of the proximal hydrophiliclayer comprises fibers of poly(ethylene-co-vinyl alcohol), the fibershaving an average diameter of about 180 nm to about 400 nm.

In one embodiment, the first fibrous polymer of the proximal hydrophiliclayer further comprises poly(hexamethylene biguanide) in the fibers ofpoly(ethylene-co-vinyl alcohol).

In one embodiment, the first fibrous polymer of the proximal hydrophiliclayer comprises fibers of poly(ethylene oxide), the fibers havinginter-fiber (interstitial) gaps of approximately 1 lam by 2.5 μm andfiber diameters of approximately 180 nm to 1.125 microns.

In one embodiment, the second fibrous polymer of the hydrophobic layercomprises fibers of poly(caprolactol), the fibers having an averagediameter of about 180 nm to about 400 nm.

In one embodiment, the second fibrous polymer of the hydrophobic layerfurther comprises fibers of poly(caprolactol) mixed with the fibers ofpoly(hexamethylene biguanide).

In one embodiment the second fibrous polymer of the hydrophobic layercomprises fibers of poly(caprolactol), the fibers having an interstitialgap size of approximately 1 μm by 2.5 μm.

In one embodiment, the second fibrous polymer of the hydrophobic layerfurther comprises poly(hexamethylene biguanide) in the fibers ofpoly(caprolactol).

In one embodiment, a distal hydrophilic layer is in contact with thehydrophobic layer opposite the proximal hydrophobic layer, the distalhydrophilic layer facilitating evaporation of liquid in the exudate fromthe wound dressing.

In one embodiment, the hydrophobic layer includes at least a first and asecond hydrophobic sub-layer, the first hydrophobic sub-layer includingfibers of poly(caprolactol) (“PCL”), hyaluronic acid (“HA”), a tri-blockcopolymer of poly(ethylene glycol) and poly(propylene glycol)(“Poloxamer 188” (poly(ethylene glycol)-block-poly(propyleneglycol)-block-poly(ethylene glycol), and sodium chloricie(“NaCl”). Thesefibers can also include varying amounts of (poly(hexamethylene biguanidehydrochloride)) (“PHMB”). A second hydrophobic sub-layer can includefibers of PEO (polyethylene oxide) and PCL (poly-caprolcatol) forming amatrix.

Embodiments also relate to a method for producing a wound dressingmaterial. A voltage difference is applied between a rotating drum of anelectro-spinner and at least one spinneret. A hydrophilic polymersolution is provided to the rotating drum through the at least onespinneret to fabricate a fibrous proximal hydrophilic layer of the wounddressing material on the rotating drum. A hydrophobic polymer solutionis provided to the rotating drum through the at least one spinneret tofabricate a fibrous hydrophobic layer in contact with the proximalhydrophilic layer. The fibrous hydrophobic layer includes inter-fibergaps for receiving exudate from a wound via the fibrous proximalhydrophilic layer when a portion of the wound dressing material isplaced on the wound. The fibrous hydrophobic layer inhibits lateraldiffusion of the exudate within the wound dressing material.

In one embodiment, the hydrophilic polymer solution has a viscosity ofbetween 200 centiPoise and 400 centiPoise.

In one embodiment, the hydrophobic polymer solution has a viscosity ofbetween 200 centiPoise and 400 centiPoise.

In one embodiment, the fibrous proximal hydrophilic layer comprisesfibers having a diameter of between 180 nm and 400 nm.

In one embodiment, the fibrous hydrophobic layer comprises fibers havinga diameter of between 180 nm and 400 nm.

In one embodiment, the method further includes adding hyaluronic acid tothe hydrophilic polymer solution before providing the hydrophilicpolymer solution to the rotating drum.

In one embodiment, the method further includes adding hyaluronic acid tothe hydrophobic polymer solution before providing the hydrophobicpolymer solution to the rotating drum.

In one embodiment, the method further includes the fibrous hydrophobiclayer having interstitial gaps with a size of 1 μm by 2.5 μm

In one embodiment, the method further includes placing an occlusive filmon the rotating drum before providing the hydrophilic polymer solutionto the rotating drum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional diagram of a conventional wound dressing.

FIG. 2 is a cross-sectional diagram of a wound dressing structured toprevent lateral diffusion of exudate, according to one embodiment.

FIG. 3 is a flowchart illustrating a process of fabricating a wounddressing, according to one embodiment.

FIGS. 4A, 4B, and 4C are photo-micrographs illustrating experimentalresults of fibers at different portions of the wound dressing and atdifferent stages of exudate absorption, according to one embodiment.

The figures depict various embodiments for purposes of illustrationonly. One skilled in the art will readily recognize from the followingdiscussion that alternative embodiments of the structures and methodsillustrated herein may be employed without departing from the principlesdescribed herein.

DETAILED DESCRIPTION

Embodiments relate to a wound dressing that does not merely absorbexudate from a wound, but rather traps the exudate in gaps betweenhydrophobic fibers in the wound dressing. This trapping prevents lateraldiffusion of the exudate through the bandage to healthy portions of theskin, thereby reducing the exposure of healthy skin to exudate andlowering the risk of maceration or infection of the healthy skin.Material of a wound dressing may be fabricated by providing solutions ofa hydrophobic polymer and a hydrophilic polymer to a rotating drum of anelectro-spinner.

FIG. 2 is a sectional diagram of a wound dressing 100, according to oneembodiment. The wound dressing 100 absorbs and traps exudate, therebypreventing the exudate from contacting healthy skin or at least reducingthe exposure of healthy skin to the exudate compared to conventionalwound dressings. The wound dressing 100 may include, among other layers,a proximal hydrophilic layer 104, a hydrophobic layer 116, a distalhydrophilic layer 118 and a protective layer 122. The proximalhydrophilic layer 104 may be coated with a medicine or a substance 102beneficial to healing of a wound (e.g., mineral oil). The wound dressing100 may also include other layers not illustrated in FIG. 2.

The proximal hydrophilic layer 104 absorbs exudate from the wound andprovides the exudate to the hydrophobic layer 116. Because the proximalhydrophilic layer 104 includes hydrophilic polymers, the exudate isreadily absorbed thereby reducing the residence time of the exudate inthe wound. This in turn reduces the risk of maceration of the woundtissue by the exudate and also reduces the risk of infection bybacterially contaminated exudate.

In one embodiment, the proximal hydrophilic layer 104 is made ofpoly(ethylene-co-vinyl-alcohol) (“EVOH” having a mer chemicalcomposition of (CH₂CHOH)). In this embodiment, the vinyl alcohol groupsprovide the hydrophilicity of the proximal hydrophilic layer 104,although any hydrophilic polymer capable of being spun or fabricatedinto a fibrous structure can also be used. Alternative hydrophilicpolymers can also be used in the proximal hydrophilic layer 104.

In another embodiment, the hydrophilic polymer used in the proximalhydrophilic layer 104 is embedded with poly(hexamethylene biguanidehydrochloride) (“PHMB” having a mer chemical composition of (C₈H₁₇N₅)).In this embodiment, PHMB is spun into the proximal hydrophilic layer 104as described below in FIG. 3, thereby becoming a component of the fibersforming the hydrophilic polymer and preventing and/or suppressing growthof bacteria in the exudate within the wound dressing 100. Other similaranti-bacterial additives can be used in the wound dressing 100, whetherincorporated into the polymer fibers of the wound dressing 100 orotherwise applied to or mixed with the fibers. Examples of alternativeanti-bacterial additives include silver, and polyamineopropinolbiguanide.

Similarly, hyaluronic acid can be added as a component of the fibers ofthe proximal hydrophilic layer 104 as described in method 300 in FIG. 3.“Hyaluronic acid” includes the corresponding metal salts of hyaluronicacid, including, for example, sodium hyaluronate (the sodium salt),potassium hyaluronate, zinc hyaluronate, magnesium hyaluronate, andcalcium hyaluronate (generally known as hyaluronic acid). Byincorporating hyaluronic acid into the fibers of the proximalhydrophilic layer 104 (and/or into the fibers of the hydrophobic layer116), the hyaluronic acid can be provided to the wound in a controlledway, thereby facilitating healing and reducing scarring by displacingcollagen at the wound. The wound dressing 100 releases hyaluronic acidin a controlled way as exudate is absorbed into the wound dressing. Thatis, as exudate is absorbed by the wound dressing 100, the exudatedisplaces hyaluronic acid in the fibers of the wound dressing 100,thereby allowing the dressing 100 to provide the hyaluronic acid to thewound progressively as exudate is received by the dressing. This, unlikeconventional applications of hyaluronic acid where a bulk application isused, does not flood or occlude the wound with hyaluronic acid, whichcan slow healing.

Furthermore, the inclusion of hyaluronic acid in fibers of the dressingincreases the tensile strength of the EVOH fibers. In some examples, upto 50 wt. %/wt. % of hyaluronic acid is added to the PCL. In addition tothe beneficial healing effects, the mechanical properties and durabilityof the proximal hydrophilic layer 104 are further improved. Afterexudate is absorbed by the proximal hydrophilic layer 104, thehydrophobic layer 116 can absorb the exudate from the proximalhydrophilic layer and trap the exudate in inter-fiber gaps with minimal,if any, lateral diffusion of the exudate in either the proximalhydrophilic layer 104 or in the hydrophobic layer 116. It may be thatthe exudate is trapped in the inter-fiber gaps through anelectrochemical interaction between at least some of the exudate and thehydrophobic polymer fibers. Surface tension or other similar forces mayalso contribute to trapping exudate in these gaps. Regardless of themechanism, this attraction between the fibers of the dressing 100 andmodel exudate has been observed using an optical microscope at amagnification of approximately 100× by placing a fiber proximate to theexudate and observing the flexure of the fiber toward the exudate.

Because exudate is trapped in gaps between the polymer fibers, thelateral diffusion of the exudate from the wound 16 to healthy portionsof skin 18 is significantly reduced. The model exudate used in this casehad a composition of sodium chloride and calcium chloride containing 142mmol/liter of sodium ions and 2.5 mmol/liter of calcium ions, which arevalues typical found in serum and wound fluid. Model exudate is used tomimic a standard wound pH (pH 6.7-7.9). It will be appreciated that thiscomposition is only one of an infinite variety of exudate that can beproduced by a wound.

One benefit of selecting a polymer having an interaction with exudate isthat the polymer fibers are drawn toward each other as the inter-fibergaps are filled with exudate. This phenomenon can cause up toapproximately a 20% reduction in the volume of the wound dressing 100,thereby reducing pressure on the wound and preventing further irritationof the wound by the wound dressing.

The hydrophobic layer 116 in this embodiment can be fabricated byelectro-spinning and/or producing fibers of the poly(caprolactol)(“PCL”) that are embedded with PHMB. These fibers can also be combinedwith elctrospun fibers of EVOH embedded with PHMB (in a concentration offrom about 0.2% through about 0.5% for antimicrobial effect) and canalso be combined with fibers of poloxamer (a tri-block copolymer havinga central hydrophobic segment (e.g., poly(propylene oxide) surrounded byterminal hydrophilic segments (e.g., PEO), such as P188). The PEO andEVOH fibers can be combined with PCL having a mer chemical compositionof (C₆H₁₀O₂). An example method of fabrication is described in moredetail in FIG. 3.

One of many benefits of combining PEO and/or EVOH fibers with PCL fibersis that the mechanical integrity of the wound dressing 100 is improvedbecause the PCL fibers have a higher modulus and a higher tensilestrength than PEO and EVOH. This allows for removal of the wounddressing 100 from the wound in a single piece without leaving fragmentsof the wound dressing in the wound and helps reduce the risk ofinfection and/or scarring of the wound. Improved mechanical integrityalso allows for improved handling of the dressing because the dressing100 is not damaged by routine handling. Another benefit of combiningfibers in this way is that the creation of interstitial (and in thisexample repository) gaps between the fibers in the hydrophobic layer 116(which can trap exudate as described above) is facilitated. Theseinterstitial gaps have approximate volumes of between 1 cubic micron and2 cubic microns. A benefit of combining PCL fibers with EVOH fibers inthe hydrophobic layer 116 is that the combination facilitates moisturevapor transmission via the gaps between the fibers in the layer. Thiscan improve oxygen transport to the skin through the dressing 100 andcan reduce the amount of exudate in the dressing. One alternative to PCLused to improve the structural integrity of the wound dressing 100 ishyaluronic acid. When incorporated into the polymer fibers, thehyaluronic acid increases the tensile strength of the fibers, therebyimproving the structural integrity of the wound dressing 100.

In the embodiment of the wound dressing 100 shown in FIG. 2, thehydrophobic layer 116 includes multiple sub-layers including an innersub-layer 108, a middle sub-layer 110 and an outer sub-layer 114. In theembodiment shown, the inner sub-layer 108 and the outer sub-layer 114include higher concentrations of PCL and a lower concentration ofPEO/PHMB relative to the middle sub-layer 110. The higher concentrationof PEO in the middle sub-layer 110 allows for the middle sub-layer tostore the bulk of exudate from a wound, whereas the lower concentrationof PEO at the inner and outer sub-layers 108 and 114 allows for vaportransport of the exudate to the middle sub-layer 110 from the proximalhydrophilic layer 104 and from the middle sub-layer 110 to the air.

While the foregoing discussion and FIGS. 1 and 2 refer to “layers” ofthe wound dressing 100, the use of this term and the depiction in FIG. 2of well-defined boundaries is for convenience and clarity ofexplanation. The boundaries between these layers are not as well definedas shown in FIG. 2, but rather transition from one composition toanother as a function of the electro-spinning process used to fabricatethe dressing 100.

The foregoing discussion also refers to various example polymersconvenient for preventing the migration of exudate from the wound tohealthy portions of skin. In addition to the hydrophilicity andhydrophobicity of the example polymers presented above, another factorin the selection of polymers for use in the wound dressing 100 is thestability of a polymer at various pH values. For example, the pH of anacute wound at hemostasis is approximately 6.2. The wound becomes moreacidic during the inflammatory stage of wound healing, steadilyincreasing during granulation and returning an approximately neutral pHduring the final stages of re-epithelialization. The pH of chronicwounds arrested in the inflammatory stage of wound healing averagearound 7.5 with considerable variation. Therefore, depending on the typeof wound and the intended use of the dressing, pH of the wound duringhealing may be included as one factor used for selecting a polymer forthe wound dressing 100.

The wound dressing 100 may further include a distal hydrophilic layer118. The distal hydrophilic layer 118 may be made of a combination ofPEO, EVOH, and PHMB. In some examples, the distal hydrophilic layer 118can be placed adjacent to the wound 16 instead of the proximalhydrophilic layer 104. That is, the symmetric configuration of the wounddressing 100 allows either the proximal or the distal hydrophilic layerto come in contact with the wound without altering the function of thewound dressing. Furthermore, the wound dressing 100 may also include asurface protective layer 122 made of a thermoplastic (such aspoly(urethane)) that can be either non-occlusive or semi-occlusivedepending on thickness.

FIG. 3 is a flowchart illustrating a process 300 for fabricating thewound dressing 100, according to one embodiment. In this embodiment, thehydrophilic layers 118, 104 and the hydrophobic layer 116 are fabricatedusing an electro-spinning process.

Solutions of the polymers used to form the wound dressing 100 areprepared 304 by dissolving the desired polymers in a solvent appropriatefor electro-spinning For example, EVOH, and PCL can be dissolved inethyl alcohol, methyl alcohol, chloroform, or combinations thereof. Theconcentration of the solution can be varied to achieve a viscosity ofthe solution (which is dependent on the molecular weight of the polymerand the strength of the solvent) appropriate to the electro-spinningvoltage and device configuration, but solutions typically have aconcentration of between 10 wt. % and 20 wt. %.

As described above, PHMB can be dissolved in the constituent solutionfor the proximal hydrophilic layer 104 and/or the hydrophobic layer 116to provide an anti-microbial effect to the wound dressing 100.Similarly, hyaluronic acid can also be added to one or more constituentsolutions used to produce fibers that include hyaluronic acid, thefibers thereby releasing the acid to the wound as the exudate isabsorbed, as described above in the context of FIG. 2. Mineral oil mayalso be dissolved in a constituent solution as another supplement thatcan enhance healing of the wound.

Up to about 0.06 wt. % of NaCl is added to the constituent solutionsalong with 0.5 wt. % of a poloxamer, such as P188 (i.e., having amolecular weight of 18,000 g/mol, and being 80% poly(oxyethylene)). Theaddition of the NaCl and the poloxamer facilitate the electro-spinningof the constituent solutions at even relatively low viscosities. Forexample, upon addition of these components, the viscosities of theconstituent solutions can be as low as 200 to 400 centiPoise. A benefitof using solutions at this low viscosity for electro-spinning is thatfibers with nano-scale diameters (e.g., at or less than about 180 nm)can be achieved using otherwise conventional electro-spinning methods.

To create a jet of the constituent solutions that ultimately forms thepolymer fibers of the wound dressing 100, spinnerets are set 308 inconductive holders around a conductive drum. The conductive drum canhave a diameter of between 200 cm and 500 cm and is placed between 10 cmand 20 cm away from the spinnerets. This configuration is used to spinfibers from the constituent solutions as described herein. In thisexample, the inner diameter of the outlet port of a spinneret isapproximately 0.06 cm in diameter, but can be bigger or smallerdepending on the constituent solution concentration and the desiredfiber diameter. Prior to fabricating the fibers from solution, anocclusive film (e.g., polyurethane film) may optionally be applied 312to the drum prior to the electro-spinning deposition of the fibers. Theocclusive film can be used as some, or all, of the protective layer 122of the wound dressing 100.

An electrical potential of from about 25 kV to about 40 kV is applied316 to the conductive solutions and the conductive drum, therebycreating an electric field at a tip of the spinnerets (also known as“capillary tubes”). As a result of this electric field, the surface ofthe fluid at the tips of the spinnerets elongates to form a conicalshape known as a Taylor Cone. As the electrical field is increased, therepulsive electrostatic force overcomes the surface tension of thesolution within the capillary tube and a jet of fluid is ejected fromthe Taylor Cone at the tip of the capillary tube. The discharged polymersolution jet, flowing at a rate of between 10 milliliters/hour and 30milliliters/hour undergoes a whipping process in the zone between thecone and the drum where the solvent evaporates leaving behind a fiberthat lays itself randomly on the rotating metal drum and forms the fibermatrix material from which the wound dressing is made 100.

The concentration of the constituent solutions and/or the flow rate ofthe solutions from the spinnerets can be controlled to spin fibers of adesired diameter. For example, solutions having a concentration of fromabout 2 wt. % to about 12 wt. % of polymer (the polymer having amolecular weight of about 200,000 g/mol) in solvent and flowed through aspinneret from about 0.2 milliliters/min to about 0.5 milliliters/mincan be used to produce fibers having an approximate diameter from about100 nm to about 2200 nm. In general, the smaller the diameter of thefiber, the more hydrophobic the fiber as indicated by a water contactangle measurement. For example, fibers produced according to the method300 having an average diameter of about 2200 nm exhibit a (water)contact angle of about 120°, whereas fibers having an average diameterof about 600 nm exhibit a contact angle of about 125°. For fibers havingaverage diameters of less than approximately 600 nm, the contact angleexhibited, and therefore the surface energy, increases at a higher rate.For example, fibers having an average diameter of approximately 400 nmto approximately 180 nm exhibit contact angles of between approximately130° to about 150° respectively. A higher surface energy of the fibersis beneficial for trapping exudates at inter-fiber gaps.

In one example, a solution of PEO, EVOH, and PHMB is deposited 320 asspun fibers on the drum, thereby forming the distal hydrophilic layer118 fibers on the optional occlusive film placed the rotating drum.Subsequently, a solution including EVOH, PEO and PHMB is deposited 324as fibers at the same time a PCL solution is injected 328 to deposit thehydrophobic layer 116 onto distal hydrophilic layer 118. The injectionrate of PCL and PEO/PHMB may be varied during this step to form threesub-layers 108, 110, 114 of different PCT and PEO/PHMB weight or volumefractions, as described above.

Then a solution including PEO, EVOH, and PHMB is deposited 332 on thedrum as spun fibers to form the proximal hydrophilic layer 104 on theinjected hydrophobic layer 116. Mineral oil or other substance can thenoptionally be applied to the hydrophilic layer to form the layer 102.The wound dressing 100 can then be removed from the drum.

FIGS. 4A, 4B, and 4C illustrate results from an experiment offabricating and using the wound dressing 100 described above. FIG. 4A isa photograph of a section of a wound dressing prepared using the method300. Specifically, the wound dressing shown in FIG. 4A was prepared byfirst preparing a 15 wt. % solution of the foregoing polymers andadditives in a mixture of chloroform and methanol. In this example, thePEO and PCL each have molecular weights of about 200,000 g/mol. The PEOfurther includes 27 mol. % of EVOH. The solutions included approximately0.06 wt. % of NaCl and 0.5 wt. % of poloxamer P188.

The constituent solutions were placed in spinnerets having an outletinner-diameter of 0.06 cm and an outlet outer-diameter of 0.09 cm. Thesolution was delivered through the spinnerets to a rotating drum at arate of approximately 0.5 milliliters/minute and at a voltage of fromabout 20 kV to about 40 kV. The drum was rotated to produce a wounddressing 100 as described above having inter-fiber gaps used to trapexudate.

The wound dressing 100 was exposed to a sample exudate solution ofsodium/calcium chloride containing 142 mmol/liter of sodium ions and 2.5mmol/liter of calcium ions. These values are typical of those found inserum and wound fluid. Solutions in this compositional range areestablished to meet a standard wound pH (pH 6.7-7.9). This exudate wasused merely for convenience and, as mentioned above, the variety ofexudate compositions is nearly infinite, being a function of at least,an individual's body chemistry, wound type, and other factors.

After exposure to exudate, the micrograph 400 was captured at amagnification of 100× using scanning electron microscope. To the left ofline A-B 404 is a region 408 of the wound dressing 400 unexposed toexudate either directly (by physical contact with the exudates at itssource) or indirectly (as absorbed by and transported through the wounddressing). To the right of line A-B 404 is a region 412 exposed toexudate that has been absorbed. The conditions under which this exposurewas performed are described above.

FIGS. 4B and 4C are 1000× magnifications of regions 408 and 412respectively. As shown in FIGS. 4B and 4C and described above in thecontext of FIG. 2, the hydrophobic layer 116 retained exudate in theinter-fiber gaps of the wound dressing shown. This is unlike theunexposed region 408, in which the inter-fiber gaps remained empty ofexudate. This phenomenon inhibited lateral diffusion of the exudatewithin the wound dressing and also reduced the volume of the wounddressing by approximately 20%.

While particular embodiments and applications have been illustrated anddescribed, it is to be understood that the disclosed embodiments are notlimited to the precise construction and components disclosed herein.Various modifications, changes and variations, which will be apparent tothose skilled in the art, may be made in the arrangement, operation anddetails of the method and apparatus disclosed herein without departingfrom the spirit and scope defined in the appended claims.

1. A wound dressing comprising: a proximal hydrophilic layer fabricatedfrom a first fibrous polymer and configured for placement adjacent to aportion of skin producing exudate to absorb the exudate; and ahydrophobic layer having a first side in contact with the proximalhydrophilic layer and a second side opposite the first side, thehydrophobic layer comprising a second fibrous polymer including fibersthat comprise fibers of poly(caprolactol) and poly(hexamethylenebiguanide hydrochloride) in the fibers of poly(caprolactol), the secondfibrous polymer configured for receiving the exudate absorbed by theproximal hydrophilic layer and storing the exudate at inter-fiber gapsto inhibit lateral diffusion of the exudate in the wound dressing. 2.The wound dressing of claim 1, wherein the second fibrous polymer of thehydrophobic layer undergoes a volume reduction upon storing the exudateat interstitial gaps.
 3. The wound dressing of claim 1, wherein thefirst fibrous polymer of the proximal hydrophilic layer comprises fibersof poly(ethylene oxide) and poly(ethylene-co-vinyl alcohol), the fibershaving an average diameter of about 180 nm to about 400 nm.
 4. The wounddressing of claim 3, wherein the first fibrous polymer of the proximalhydrophilic layer further comprises poly(hexamethylene biguanide) in thefibers of poly(ethylene-co-vinyl alcohol).
 5. The wound dressing ofclaim 1, wherein the first fibrous polymer of the proximal hydrophiliclayer comprises fibers of poly(ethylene oxide) andpoly(ethylene-co-vinyl alcohol), the fibers having an interstitial gapsize of between 1 micron and 2.5 microns.
 6. The wound dressing of claim1, wherein the second fibrous polymer of the hydrophobic layer comprisesfibers of poly(caprolactol), the fibers having an average diameter ofabout 180 nm to about 400 nm.
 7. The wound dressing of claim 6, whereinthe second fibrous polymer of the hydrophobic layer further comprisesfibers of poly(ethylene-co-vinyl alcohol) mixed with the fibers ofpoly(caprolactol).
 8. The wound dressing of claim 1, wherein the secondfibrous fibers of poly(caprolactol) of the second fibrous polymer havean interstitial gap size of between 1 micron and 2.5 microns. 9.(canceled)
 10. The wound dressing of claim 1, further comprising adistal hydrophilic layer in contact with the hydrophobic layer oppositethe proximal hydrophobic layer, the distal hydrophilic layerfacilitating evaporation of liquid in the exudate from the wounddressing.
 11. The wound dressing of claim 1, wherein the hydrophobiclayer includes at least a first and a second hydrophobic sub-layers, thefirst hydrophobic sub-layer comprising fibers of poly(caprolactol) thatinclude hyaluronic acid, sodium chloride, and a tri-block copolymer ofpoly(ethylene glycol) and polypropylene glycol), and the secondhydrophobic sub-layer comprising fibers of poly(ethylene oxide) andpoly(caprolactol). 12-20. (canceled)
 21. The wound dressing of claim 1,wherein the fibers of the first fibrous polymer include fibers thatcomprise at least one polymer and hyaluronic acid.
 22. The wounddressing of claim 21, wherein the fibers of the first fibrous polymerare configured to release hyaluronic acid as exudate is absorbed.
 23. Awound dressing comprising: a proximal hydrophilic layer fabricated froma first fibrous polymer and configured for placement adjacent to aportion of skin producing exudate to absorb the exudate, the firstfibrous polymer of the proximal hydrophilic layer comprising firstfibers of poly(ethylene oxide) and second fibers poly(ethylene-co-vinylalcohol), the first fibers and the second fibers having an interstitialgap size of between 1 micron and 2.5 microns; and a hydrophobic layer incontact with the proximal hydrophilic layer, the hydrophobic layercomprising a second fibrous polymer configured for receiving the exudateabsorbed by the proximal hydrophilic layer and storing the exudate atinter-fiber gaps to inhibit lateral diffusion of the exudate in thewound dressing.
 24. The wound dressing of claim 23, wherein a volume ofthe fibrous hydrophobic layer is reduced as the exudate is stored atinterstitial gaps of the fibrous hydrophobic layer.
 25. The wounddressing of claim 23, wherein the hydrophobic layer comprises fibers ofpoly(caprolactol) of the first hydrophobic sub-layer further comprisepoly(hexamethylene biguanide hydrochloride) in the fibers ofpoly(caprolactol).
 26. The wound dressing of claim 23 wherein thefibrous polymer of the proximal hydrophilic layer comprisespoly(hexamethylene biguanide) in fibers of poly(ethylene-co-vinylalcohol).
 27. The wound dressing of claim 23, further comprising adistal hydrophilic layer in contact with the fibrous hydrophobic layerand locate opposite to the proximal hydrophilic layer, the distalhydrophilic layer configured to facilitate evaporation of liquid in theexudate from the wound dressing.
 28. The wound dressing of claim 1,further comprising a non-occlusive surface protective layer adjacent tothe second side of the hydrophobic layer.
 29. The wound dressing ofclaim 1, further comprising a semi-occlusive surface protective layeradjacent to the second side of the hydrophobic layer.